Method for cleaning filters

ABSTRACT

In a method and apparatus for cleaning filters, the cleaning is efficiently performed by selecting cleaning steps according to the degree of contamination of the filter media. The degree of contamination of the filter media is analyzed before the filter is carried into the cleaning apparatus. Filters with heavily contaminated filter media are subjected to pretreatment before the cleaning process is performed, and the filters with less contaminated filter media are directly subjected to the cleaning process. The cleaned filter is subjected to a restoration process before reuse.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forcleaning filters, such as air intake filters, ventilation air filterscontaminated with dust and other particles, etc.

[0003] 2. Description of the Related Art

[0004] Filters are used in various fields to remove dust and otherparticles from fluid such as air. For example, medium performancefilters are used for air passages in air conditioning systems inbuildings or underground shopping malls, and are used in air intakelines of devices such as local gas turbine generators. These filters areused to remove salts, dust, oil particles, fibers and other substances(hereafter collectively referred to as “contaminants”) from the air bycollecting them on a filter media of resin fiber or other materials.

[0005]FIGS. 10a and 10 b show a perspective view of such filters. Thefilter F shown in FIG. 10a has a filter media f with a corrugated nonwoven fabric of resin fibers or of glass fibers, folded in parallel tothe corrugation in zigzag pattern and retained within a frame 51. Thefilter F shown in FIG. 10b has a filter media f folded in zigzag patternwith corrugated separators f(a) inserted between folded filter media andretained within the frame 51.

[0006] As an apparatus for cleaning such filters, the applicant hasfiled a patent application of an ultrasonic cleaning apparatus (JapaneseLaid-Open Patent Publication No. Hei 9-276633). In this apparatus, acontaminated filter accommodated on a rack is conveyed by a handlingunit to an ultrasonic cleaning tank for cleaning, and a cleaned filteris rinsed in a rinse tank and returned to the rack.

[0007] However, filters F cannot always be cleaned under the samecondition because the degree of contamination of such filters variesaccording to their conditions of usage and other factors. For instance,when all filters are cleaned in the condition needed for cleaningheavily contaminated filters, a considerable time loss occurs in thecleaning of less contaminated filters.

[0008] On the other hand, when all filters are cleaned in the shortperiod of time needed for cleaning of less contaminated filters,sufficient cleaning effect is not obtained for the heavily contaminatedfilters, and cleaning of the internal portion of the filter media issometimes difficult.

[0009] Moreover, as filters F has a frame surrounding a complicatedfilter media, contaminants removed from the filter media tend toreattach on the cleaned filter media, which sometimes makes difficultthe complete removal of contaminants.

[0010] It is therefore an object of the present invention to provide amethod and apparatus for cleaning filters in accordance with the degreeof contamination.

SUMMARY OF THE INVENTION

[0011] In the filter cleaning method according to the present invention,the degree of contamination of the filter media is analyzed to selectthe cleaning steps of the filter according to the degree ofcontamination. Heavily contaminated filters are subjected topretreatment before cleaning, while less contaminated filters arecleaned without pretreatment, and cleaned filters are subjected to arestoration process for preventing decrease in thickness of the filtermedia after drying. The pretreatment can be performed by a method suchas immersing the filter in a pretreatment solution containing adetergent. The restoration can be performed by a method such asimmersing the filter media in a restoration solution containing asoftener. In this way, the necessity of performing pretreatment isdetermined according to the degree of contamination, therefore, theheavily contaminated filter media is cleaned effectively by the additionof pretreatment before the cleaning, while the less contaminated filtermedia is cleaned in a shorter time. Moreover, by utilizing therestoration process after the cleaning, the capturing capacity ofcontaminants per filtering area is restored to the capacity before thecleaning.

[0012] Heavily contaminated filters are preferably subjected topretreatment and to rinsing of the pretreatment liquid before thecleaning. The contaminants become easily removable by the pretreatment,and a greater part of the contaminants can be removed by the rinsing tosignificantly enhance the effectiveness of the subsequent cleaningprocess.

[0013] In addition, the sterilization of filters for use in environmentswhich will affect human beings can be performed continuously after therestoration.

[0014] Furthermore, by performing processes up to the cleaning andprocesses after the cleaning in separate systems, the processes up tothe cleaning which need longer time, and processes after the cleaningcan be performed independently, thus increasing the efficiency andreducing the time needed for performing the cleaning operation.

[0015] Ultrasonic cleaning can efficiently remove contaminants withinthe filter media.

[0016] The cleaning unit according to the present invention comprises,means for analyzing the degree of contamination of the filter media,means for arranging the filter in a predetermined location according tothe degree of contamination, means for conveying the filter from thepredetermined location, means for performing pretreatment when thefilter is classified as heavily contaminated, means for cleaning thefilter; and means for restoring the filter media for preventingreduction of thickness after the cleaning. With this filter cleaningmethod and apparatus, the degree of contamination of the filter media isfirst analyzed by the analysis means and classified according topreviously determined standards, and the filter is accommodated at thepredetermined location according to the classification. The heavilycontaminated filter is conveyed to the pretreatment process, and theless contaminated filter is conveyed directly to the cleaning process bythe conveying means. Then the filter media of the cleaned filter isrestored. Thus efficient cleaning operation can be performed byselecting the cleaning procedure according to the degree ofcontamination of the filter media. As a result, by the restoration afterthe cleaning, sufficient filtering capacity of the cleaned filter can berestored.

[0017] In addition, by providing the pretreatment rinsing means, thecleaning effect can be increased because the contaminants have becomeeasily removable by the pretreatment process and can be rinsed awaybefore the cleaning. The pretreatment rinsing means provided by apretreatment rinse tank having a flow generating means for directingrinsing liquid toward the filter media also enhances the filter cleaningeffect.

[0018] Filters for use in environments that affect human beings can besterilized after the cleaning by the sterilization means which isprovided after the restoration of the filter media.

[0019] Furthermore, by separating conveying means into two separatesystems, i.e. conveying means for conveying the filter in processes upto the cleaning of the filter, and conveying means for conveying thefilter in processes after the cleaning, cleaning of the filters whichneed a longer time can be performed simultaneously with other processessuch as a restoration process. As result, working efficiency issignificantly increased thereby reducing the total work time.

[0020] In addition, by forming the cleaning means as an ultrasoniccleaning tank, in which the filter is immersed for a specified amount oftime, the contaminants adhered on the filter media can be removedeffectively by means of cavitation created by the ultrasonic waves.

[0021] Moreover, by conveying means which comprises a filter frame forholding the filter and a conveyor unit which holds the upper portion ofthe filter frame while conveyed, the conveyor unit can be prevented frombeing wetted by the cleaning liquid during the pretreatment, cleaning orrestoration processes.

[0022] These objects as well as other objects, features and advantagesof the present invention will become more apparent to those skilled inthe art from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a perspective view of a preferred embodiment of a filtercleaning apparatus according to the present invention;

[0024]FIG. 2 is a plan view of an example of a pretreatment rinse tankshown in FIG. 1;

[0025]FIG. 3 is a front view of the pretreatment rinse tank in FIG. 2;

[0026]FIG. 4 is a side view of the pretreatment rinse tank in FIG. 2;

[0027]FIG. 5 is a flow chart showing an example of analyzing the degreeof contamination of filters to be conveyed into the filter cleaningapparatus shown in FIG. 1;

[0028]FIG. 6 is a flow chart showing processes up to a cleaning step inthe filter cleaning apparatus shown in FIG. 1;

[0029]FIG. 7 is a flow chart showing processes after the cleaning stepof the filter cleaning apparatus shown in FIG. 1;

[0030]FIGS. 8a and 8 b show a front view and a side view respectively ofa second preferred embodiment of a holding means of the conveyor unit inthe filter cleaning apparatus according to the present invention;

[0031]FIGS. 9a, 9 b and 9 c show a plan view, a side view and aperspective view, respectively, of the filter holding means in theconveyor unit in FIG. 8; and

[0032]FIGS. 10a and 10 b are perspective views of filters to be cleanedby the cleaning apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] As shown in FIG. 1, a support frame 2 of conveyor unit C1 and C2of a filter cleaning apparatus M is provided on a foundation 1 ofrectangular plane shape. Conveyor units C1 and C2 movable in thedirection X and Y are mounted on the top surface of the support frame 2.Racks 3 are provided on the foundation 1 for temporarily accommodating aplurality of filters to be cleaned and cleaned filters. The racks 3 arearranged in a plurality of lows in the width direction (X direction) toaccommodate a plurality of filters F in longitudinal direction (Ydirection), and each accommodating location is previously numbered.

[0034] Transportation of filters to the rack 3 is performed by atransporting unit (not shown) such as a crane or a conveyor belt. Thetransporting unit is provided with filter analyzer means A for analyzingthe degree of contamination of the filter media to be cleaned. Thedegree of contamination of the filter media can be analyzed by such asmeasuring a pressure drop by passing a gas through the filter media, orby measuring the weight difference of the filter between a contaminatedcondition and a non-contaminated condition. The degree of contaminationcan also be analyzed by measuring the thickness of the filter media,because the thickness of the filter media increases according to theamount of accumulated contaminants. Various other means can be employedfor analyzing the degree of contamination. The filter to be cleaned ispreliminary classified according to the degree of contamination by theanalyzing means.

[0035] On both lengthwise end portions of the foundation 1, a pluralityof tanks are arranged for performing the respective steps of cleaningfilters F. In this embodiment, a pretreatment tank 4, a pretreatmentrinse tank 5 and a tank 6 a for ultrasonic cleaning unit 6 are arrangedin the front end portion (lower left portion of FIG. 1) of thefoundation 1. A rinse tank 7, a restoration tank 8 and a sterilizationtank 9 are provided in the rear end portion (upper right portion ofFIG. 1) of the foundation 1. In this embodiment, processes up to thecleaning, i.e., processes performed in the group of tanks 4, 5, and 6 a,and processes after the cleaning, i.e. processes performed in the groupof tanks 7, 8, and 9, can be performed in separate systems, and twoconveyor units C1 and C2 are provided for conveying filter F in eachrespective system.

[0036] Conveyor units C1 and C2 are mounted respectively on arectangular conveyor frame 11 which is movable along rails 10 mounted onthe top surface of the support frame 2 in the Y direction. A conveyorcart 12 is mounted on the respective conveyor frame 11 and movable alongrails 11 a in the X direction. The conveyor frames 11 are moved in the Ydirection along the rails 10 by drive units not shown, and the conveyorcarts 12 are moved along the conveyor frames 11 in the X direction bydrive units 13. Holding means are provided on the underside ofrespective conveyor carts 12 for holding the filter F during transportand process. The holding means in this embodiment is formed as a pair ofconveyor arms 14 to hold the filter F frame in widthwise.

[0037] The conveyor arms 14 are provided on the underside of theplatform 16 which is suspended under the conveyor cart 12 and is movedvertically by a drive motor 15, and adapted to move oppositely inwidthwise with each other by a drive motor 17. A holding plate 18 isprovided between the conveyor arms 14 to hold filters F at a specifiedposition in the liquid in the respective tank. A control panel 19 isprovided for controlling these units.

[0038] The pretreatment tank 4 is provided to facilitate removal ofcontaminants adhered to the filter media f. In this embodiment, thepretreatment tank 4 is a square vessel filled with an aqueous solutioncontaining detergent as a pretreating agent. By immersing the filters Fin the aqueous solution, the detergent penetrates into the boundariesbetween contaminants and fibers of the filter media f to facilitateremoval of contaminants and thereby enhance the cleaning effect in thesubsequent cleaning process by the cleaning unit 6.

[0039] The pretreatment rinse tank 5 is provided for rinsing away thecontaminants being made easily removable by the penetration of thedetergent in the pretreatment tank 4. FIG. 2 shows an example of a planview of the pretreatment rinse tank 5. FIGS. 3 and 4 show a front viewand a side view of the pretreatment rinse tank 5. In this embodiment, aflow generator 20 is provided as a flow generating means to facilitateremoval of contaminants.

[0040] The filter F is immersed in the water in a square vessel 5 a inthe pretreatment rinse tank 5, and the flow generator 20 creates a waterflow directed toward both sides of the filter media f. Water flow iscreated on the surface of the filter media f by the water ejected fromnozzles 21 provided at lower portion of both sides of the filter mediaf. In this embodiment, two nozzles 21 are provided on each side to causewater flow to each respective face of the filter media f. The watersuctioned by a pump 22 through an intake pipe 23 provided at the bottomof the pretreatment rinse tank 5 is delivered through a pipe 24 to eachof the nozzles 21. In the figures, the water is shown as ejected fromall of the nozzles 21, but in the actual operation, the water is ejectedalternately, so that when the water is ejected form the nozzles 21 onone side, the ejection from the nozzles 21 on the other side is stopped.This is for the purpose of allowing a part of water to pass through thefilter media f for preventing recontamination of the other filter mediaside. With such rinsing, a part of water flow created by the nozzles 21can flow through the filter media f and promote removal of contaminantswithin the filter media f. The type of flow generator 20 can be selectedaccording to the size of the filter F and the thickness and shape of thefilter media f. A selector valve 24 a is provided on the pipe 24 toselect the water flow to eject from the nozzles 21 or to circulate tothe upper portion of the pretreatment rinse tank 5.

[0041] A water level sensor 25 is also provided to detect the drop ofthe water level in the pretreatment rinse tank 5. When the drop of waterlevel is detected, the water is supplied through a supply pipe 26. Inthis embodiment, the water is also delivered to the other tanks 4, 6 athrough the supply pipe 26. A drain pipe 27 is also provided.

[0042] The cleaning unit 6 is a unit that utilizes ultrasonic waves forremoving the contaminants stuck to the filter media f by a cavitationcreated by the ultrasonic waves in the cleaning liquid. The filter F isinserted from the open top of the square ultrasonic cleaning tank 6 a ofthe cleaning unit 6 and held upright in the cleaning liquid to directboth the upstream side and the downstream side of the filter media f ina horizontal direction, so that the filter media f is cleaned by theultrasonic waves generated by the ultrasonic oscillator 28 provided onthe upstream side or the downstream side of the filter F. The ultrasonicwave generated by the ultrasonic oscillator 28 creates effectivecavitation in the filter media f of the filter F held in the cleaningliquid. In this embodiment, the filter F and the ultrasonic oscillator28 do not move with respect to each other during the cleaning. Dependingon the type or other factors of the filter F, however, it is possible tomove either of them during cleaning. In this embodiment, the filter F isheld stationary at the predetermined location in the cleaning tank 6 aby the conveying arm 14 of the conveyor unit C1.

[0043] The filter media f is held in parallel to the ultrasonicoscillator 28 to face each other in the ultrasonic cleaning tank 6 a.Therefore, a filter media f with large surface area can be cleanedeffectively utilizing cavitation created by the ultrasonic waves passedthrough the filter media f and reflected on the opposite wall.

[0044] The rinse tank 7 is adapted to wash away the reattachedcontaminants once removed from the surface of the filter media f by theultrasonic cleaning unit 6. Similar to the pretreatment rinse tank 5,the rinse tank 7 also has flow generators 20 to remove contaminants onceremoved by the cleaning unit 6 and contaminants dropped from the filtermedia f and reattached on the filter F. By holding the filter Fstationary in this manner during removal of the contaminants, thereattachment of contaminants can be prevented.

[0045] The restoration tank 8 is adapted to restore filtering capacityby preventing reduction of thickness of the filter media f due to theshrinkage after cleaning. The restoration tank 8 also has a square shapeand is filled with restoration liquid. Examples of the restoration agentused in the restoration tank 8 for restoring the filter media f includenonionic surface activators, positive ion surface activators and othersofteners. The kind of restoration liquid can be selected according tothe type and thickness of the filter media f.

[0046] The sterilization tank 9 is used for sterilizing the filter Fafter the restoration, and particularly for sterilizing filters ofindoor or household use to prevent pollution with germs in environmentsthat may affect human beings. The sterilization tank 9 also has a squareshape. Ozonized water and hypochlorous acid soda may be used as thesterilization medium.

[0047]FIG. 5 is a flow chart showing steps for analyzing the degree ofcontamination of the filter which is transported into the filtercleaning apparatus. FIG. 6 is a flow chart showing steps up to cleaningof the filter by the filter cleaning apparatus. FIG. 7 is a flow chartshowing steps performed after the filter has been cleaned by the filtercleaning apparatus. The following explanation is based on the embodimentshown in FIG. 1 in which the respective processes up to the filtercleaning and processes after filter cleaning are performed as separatesystems. In this embodiment, the filters F are classified in advanceaccording to the degree of contamination, and arranged at predeterminedlocations on the rack 3 according to the classification. The filters Farranged on the same rack 3 are adapted to be sequentially cleaned underthe same condition. Other selecting steps in the flow chart aredetermined by the data preliminary entered in the control unit.

[0048] As shown in FIG. 5, the filters F are transported into the filtercleaning apparatus M by transporting unit such as a conveyor belt (stepa). The degree of contamination of the filters F is measured by thefilter analyzer means A before the filters F are conveyed into thefilter cleaning apparatus M (step b). The measured result is recorded inthe control panel or the filters F are arranged at predeterminedlocations according to the measured result (step c). In this embodiment,the filters F are classified and arranged at the predetermined locationon the rack 3 according to the degree of contamination determined by thefilter analyzer means A. The conveyor units C1 and C2 are used as themeans for conveying the filters F from the transporting unit to the rack3. When the filters F to be cleaned have been placed at thepredetermined location on the rack 3, the cleaning process can bestarted (step d) as shown in FIG. 6.

[0049] Heavily contaminated filter F is taken out from the rack 3 (stepe) by the conveyor arm 14 of the conveyor unit C1, and if the filter Fis classified as heavily contaminated (step f) conveyed to thepretreatment tank 4 according to the degree of contamination. In thisembodiment, the filter F is already classified as heavily contaminated,the filter F is carried into the pretreatment tank 4 by the conveyorunit C1 in which the conveyor frame 11 moves in the Y direction alongthe rails 10, and the conveyor cart 12 moves in the X direction alongthe conveyor frame 11. Above the pretreatment tank 4, the filter F isdipped in the pretreatment liquid in the tank 4 by lowering conveyorarms 14. The filter F is held in the pretreatment liquid includingdetergent for a predetermined time period sufficient to allow thedetergent to penetrate through the entire surface of the filter media(step g). After the predetermined time period, the filter F is removedfrom the pretreatment tank 4 by lifting conveyor arms 14, and conveyedinto the adjacent pretreatment rinse tank 5.

[0050] Above the pretreatment rinse tank 5, the filter F is dipped inthe water in the pretreatment rinse tank 5 by lowering conveyor arms 14,and the filter F is held in the predetermined position, then, the wateris ejected from the nozzles 21 (FIG. 2) provided in the pretreatmentrinse tank 5 to wash away the detergent on the filter media f andfacilitate the removal of the pretreated contaminants (step h). Afterthe predetermined time period, the filter F is removed from thepretreatment rinse tank 5 by lifting the conveyor arms 14, and conveyedinto the adjacent cleaning unit 6.

[0051] Above the cleaning unit 6, the filter F is dipped into thecleaning liquid in the cleaning tank 6 a by lowering conveyor arms 14.When the filter F is held at the predetermined position in the cleaningtank 6 a, ultrasonic waves generated by the ultrasonic oscillator 28detach the contaminants stuck on the filter media f (step i). Theheavily contaminated filter F can be cleaned effectively, because thecontaminants comes off easily after the pretreatment. After thepredetermined time period, the filter F is removed from the cleaningunit 6 by lifting conveyor arms 14, and returned to the predeterminedlocation on the rack 3 (step j). In this embodiment, filter conveyingoperation and filter holding operation in a series of processes up tothe cleaning, i.e., step e to step j is performed by the conveyor unitC1 in a single system. By repeating operation of conveyor unit C1 inthis system, a large number of filters F can be cleaned efficiently.

[0052] As shown in FIG. 7, the cleaned filter F returned on the rack 3is taken out by conveyor arms 14 of the other conveyor unit C2 (step k).When rinsing is required (step 1), the filter F is conveyed into therinse tank 7. Above the rinse tank 7, the filter F is dipped into waterin the rinse tank 7 by lowering conveyor arm 14. As in step h, water isejected from the nozzles 21 provided in the rinse tank 7 to rinse awaythe reattached contaminants on the filter media f (step m). After thepredetermined time period, the filter F is removed from the rinse tank 7by lifting conveyor arms 14, and then the rinsed filter F is conveyedinto the adjacent restoration tank 8.

[0053] Above the restoration tank 8, the filter F is dipped into therestoration liquid in the restoration tank 8 by lowering the conveyorarms 14. Leaving the filter F in the restoration fluid for thepredetermined time period, the filter media f is restored (step n). Therestored filter F is removed from the restoration tank 8 by liftingconveyor arms 14, and if sterilization is required (step o), the filterF is then conveyed into the adjacent sterilization tank 9 and subjectedto sterilization process (step p). Filters F for use in the environmentwhere human beings work or livestock are kept, need sterilization in thesterilization tank 9. Filters F for use in industrial machinery orengines do not need sterilization.

[0054] The sterilized filter F is removed from the sterilization tank 9by lifting conveyor arms 14, and the filter F is returned to thepredetermined location on the rack 3 (step q) by the conveyor unit C2.The series of conveying and holding operations after the cleaning offilters F is performed by the other conveyor unit C2. The conveyor unitC2 repeats the process from the step k to the step g above, therefore, alarge number of filters F can be cleaned efficiently. When the series ofoperations has been completed the cleaned filter F is returned to therack 3. After the predetermined time period necessary to dry, thecleaned filter F is brought out by a transporting unit such as aconveyor belt to the filtering unit to reinstall.

[0055] In this manner, the heavily contaminated filter F can be cleanedeffectively, by subjecting to pretreatment before performing ultrasoniccleaning by the cleaning unit 6. Moreover, in this embodiment, theoperation is efficiently performed in a short period of time byutilizing two separate conveyor units C1 and C2.

[0056] The cleaning operation for the less contaminated filter isperformed by skipping the (steps g and h) as shown in FIG. 6. Also inthis case, less contaminated filters F are classified in advance andarranged at the predetermined location on the rack 3. The filter F istaken out from the rack 3 by conveyor arms 14 of the conveyor unit C1(step e), and then conveyed directly to the cleaning unit 6 by theconveyor unit C1 which moves along the rails 10 in the Y direction, andthe conveyor cart 12 which moves along the conveyor frame 11 in the Xdirection.

[0057] Above the cleaning unit 6, the filter F is dipped into thecleaning liquid filled in the ultrasonic cleaning tank 6 a by loweringconveyor arms 14 for performing ultrasonic cleaning (step i). After thepredetermined time period, the filter F is removed from the cleaningunit 6 by conveyor arms 14 and returned to the predetermined location onthe rack 3 (step j). A series of conveying operation is performed by theconveyor unit C1 as a single system.

[0058] As shown in FIG. 7, the cleaned filter F returned on the rack 3is then taken out by conveyor arms 14 of the other conveyor unit C2(step k). If rinsing is necessary (step 1), the remaining contaminant onthe filter media f is rinsed away in the rinse tank 7 (step m). Afterrinsing in the rinse tank 7, the rinsed filter F is then conveyed to theadjacent restoration tank 8.

[0059] Above the restoration tank 8, the filter F is dipped into therestoration liquid filled in the restoration tank 8 by lowering conveyorarms 14. Leaving the filter F in the restoration fluid for thepredetermined time period, the filter media f is restored (step n). Ifthe sterilization is required (step o), the restored filter F isconveyed to the sterilization tank 9 to perform a sterilization process(step p). The sterilized filter F is removed from the sterilization tank9 and conveyed by the conveyor unit C2 to the predetermined location onthe rack 3.

[0060] In this manner, the less contaminated filter F can be cleanedefficiently in a short period of time because the filter media f can besubjected to ultrasonic cleaning by the cleaning unit 6 withoutpretreatment. The filters F having been cleaned by the series of stepsare kept at a suitable place for a certain time period needed to dry,and are transported by the transporting unit (not shown) to thefiltering unit for reinstall.

[0061] According to this embodiment, the degree of contamination isanalyzed in advance and the filter F are arranged at a predeterminedlocation on the rack 3 according to the degree of contamination.Consequently, the flow of the cleaning operation can be simplified byoperating conveyor unit C1 such that the cleaning operation of filters Farranged at certain locations on the rack 3 starts from the pretreatmenttank 4, and the cleaning operation of filters F arranged at otherlocations on the rack 3 starts from the cleaning unit 6. In addition,according to this embodiment, the utilization of two conveyor units C1and C2 greatly reduces the operational time required to perform theseries of cleaning operations, because while the filter F to be cleanedis conveyed by one conveyor unit C1 into the cleaning unit 6 to performthe time consuming cleaning process, the cleaned filter F on the rack 3is conveyed by other conveyor unit C2 into the rinse tank 7 to performrinsing and subsequent process. As a result, the time required for theseries of cleaning operations can be reduced greatly by the simultaneousoperations of the two conveyor units C1 and C2.

[0062] The control panel 19 can be configured to monitor the temperatureand quantity of the water in the cleaning unit 6 or to monitorcontamination of the cleaning fluid according to the type of the filterF or the degree of its contamination.

[0063] In this embodiment, two conveyor units C1 and C2 are provided toefficiently clean filters, however, the conveying and holding operationof the entire cleaning process can be performed by a single conveyorunit when a small number of filters are cleaned. Thus the presentinvention is not intended to be limited to the embodiment describedabove.

[0064]FIG. 8 shows a second embodiment of the conveyor unit in thefilter cleaning apparatus according to the present invention. FIG. 8ashows a front view and FIG. 8b shows a side view. FIG. 9 shows a filterretaining element of the conveyor unit shown in FIG. 8. FIG. 9a shows aplan view, FIG. 9b shows a side view and FIG. 9c shows a perspectiveview of the holding element. As shown in the figures, the filter F isretained to a filter retaining frame 29, and the retaining frame 29 isconveyed by the conveyor units C1 and C2 (FIG. 1).

[0065] As shown in FIG. 8a, the filter retaining frame 29 comprises aframe body 30 formed by frame members 30 a which surround both sides andthe bottom of the filter F, a rail member 30 b which connects the upperportions of the frame members 30 a, hold members 30 c being movablealong the rail member 30 b; and suspension members 31 having latchingmembers 31 b which suspend the rail member 30 b at both sides of theframe member 31 a. The frame body 30 has a square shape in plan view asshown in FIG. 9a. The latching members 31 b can swing outward, and areswung downward when the rail member 30 is suspended such that both endsof the rail member 30 are inserted into latching holes 31 c (FIG. 9c) ofthe latching members 31 b from left and right sides to support the railmember 30 b, as shown in the two dotted chain lines in FIG. 8a.

[0066] With the filter retaining frame 29 of this configuration, thesuspension member 31 is held by the platform 16 which is raised andlowered by the drive motor 15 in the same mariner as the aforementionedconveyor units C1 and C2, so that the filter F is raised and loweredtogether with the frame body 30. Consequently, the filter F held by thisfilter retaining frame 29 can be processed without dipping the lower endportion of the conveyor unit such as conveyor arm 14 into the liquid inthe tanks. Moreover, in this embodiment, the filter F is retained insuspended condition, the size of the tanks can be reduced widthwisemaking the whole unit more compact

[0067] Adoption of this type of suspension means can be made inaccordance with the type of filter F and the cleaning method, and thepresent invention is not intended to be limited to the preferredembodiment described above.

[0068] Numerous modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, this description is to be construedas illustratively only, and is provided for the purpose of teachingthose skilled in the art the best mode of carrying out the invention.The details of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention and all modificationswhich come within the scope of the appended claims are reserved.

What is claimed is:
 1. A method for cleaning a contaminated filterincluding a filter media comprising steps of: analyzing a degree ofcontamination of the filter media for selecting cleaning steps accordingto the degree of contamination; pretreating the filter whose filtermedia is analyzed as heavily contaminated; cleaning the filter media;and restoring the filter media for preventing the reduction of thethickness of the cleaned filter media.
 2. The method according to claim1, wherein rinsing is performed after said pretreating step of theheavily contaminated filter media and before said cleaning step.
 3. Themethod according to claim 1, wherein a sterilizing step is performedafter said restoring step.
 4. The method according to claims 1, whereinprocesses up to said cleaning step and processes after said cleaningstep are performed in separate systems.
 5. The method according toclaims 1, wherein said cleaning step is performed by ultrasoniccleaning.
 6. A filter cleaning apparatus for cleaning contaminatedfilter including a filter media comprising: means for analyzing a degreeof contamination of the filter media; means for arranging said filter ata predetermined location in the filter cleaning apparatus according tothe degree of contamination; means for conveying said filter from saidpredetermined location; means for performing pretreatment of a filtermedia classified as heavily contaminated; means for cleaning said filtermedia; and means for restoring the filter media for preventing reductionof thickness after the cleaning.
 7. The apparatus according to claim 6,wherein said apparatus is provided with pretreatment rinsing means forrinsing the pretreated filters.
 8. The apparatus according to claim 7,wherein said pretreatment rinsing means comprises a pretreatment rinsetank filled with rinsing liquid, and a flow generating means fordirecting rinsing liquid toward the filter media.
 9. The apparatusaccording to claim 6, wherein said apparatus includes sterilizing meansfor sterilizing restored filter media.
 10. The apparatus according toclaim 6, wherein said conveying means are separately provided forconveying filters up to said cleaning means, and for conveying saidcleaned filter.
 11. The apparatus according to claim 6, wherein saidcleaning means is formed as an ultrasonic cleaning tank.
 12. Theapparatus according to claim 6, wherein said conveying means includes: aframe for holding said filter and a holding means for holding said frameat an upper portion thereof while said filter is conveyed.